...it's a lunar rainbow!
I saw this picture taken by Martin McKenna on Spaceweather.com today. It was a rainbow lit not by the sun, but by the moon! A "moonbow" is usually high cirrus clouds lit by the moon (or ice crystals high in the sky), creating a halo. I don't have a picture handy of that, but experienced it many times during cold New England winters.
I've never seen this but hope to. Incredible!
~L
